The present invention relates to a lens pad, a lens pad manufacturing method, a lens manufacturing method, and an adhesive member.
Techniques for water-repellent finishing on the surfaces of various substances are known. When the surface of a substance undergoes a water-repellent treatment, its surface energy decreases and this inhibits adhesion of other substances onto the surface. Hence, a water-repellent surface exhibits not only a water-repellent effect but also an excellent antifouling performance. Also, because a water-repellent surface cannot strongly stick and hold the adhering substances, even dirt adhering on the surface can be removed easily. Moreover, because a water-repellent surface has a relatively low coefficient of friction, it feels smooth when one directly or indirectly touches it with his or her finger.
However, since a water-repellent surface inhibits adhesion of other substances, it naturally inhibits adhesion of adhesive tape as well. In other words, even when adhesive tape is attached onto a water-repellent surface, it readily peels off. In addition, when a force acts on the adhesive surface of the adhesive tape in the direction of shearing, the adhesion of the adhesive tape on the water-repellent surface is readily released, and the attachment portion of the adhesive tape is consequently prone to shift.
One example of the water-repellent finishing target is spectacle lenses. Some kinds of spectacle lenses have undergone water-repellent finishing so as to prevent, e.g., sebum contamination attributed to a touch with the fingers and dust particle contamination. A lens manufacturing process in which such a lens is framed in a spectacle frame includes a step of attaching adhesive tape onto a water-repellent surface. Furthermore, in this step, a heavy load is imposed on the adhesive interface. Details of this step will be described below.
A spectacle lens is manufactured by grinding or cutting the peripheral surface of a round lens (to be also referred to as a target lens or simply referred to as a lens hereinafter) by a rotary edging tool such as a grindstone or a cutter based on the edge shape data of a spectacle frame to shape the lens into an edge shape conforming to the shape of the spectacle frame. Edging of a spectacle lens needs not only to conform to the shape of a frame but also to produce optical characteristics involved at positions that follow the owner's prescriptions concerning, e.g., his/her focal position and cylinder axis. In other words, specific regions on a target lens must be shaped into specific shapes.
Japanese Patent Laid-Open No. 2007-268706 (patent reference 1) describes shaping (edging) of a target lens by a grindstone or a cutter while clamping the convex and concave surfaces of the target lens at the edging center portion using an edging jig attached on a lens rotating shaft. The edging jig includes a lens holder onto which the convex surface of the lens is fixed, and a lens retainer which presses the concave surface of the lens. A lens pad including adhesive layers on its both surfaces is inserted between the lens holder and the lens, and the lens is fixed onto the lens holder by the adhesive force of the pad. When the lens is stably fixed, it can be shaped into a specific edge shape.
However, it is difficult to stably attach the above-mentioned pad onto a water-repellent lens. Furthermore, when a water-repellent lens is shaped into a specific edge shape using a rotary edging tool, a shearing force is inflicted on the interface between the adhesive surface of the pad and the lens surface. Under such demanding conditions, the attachment position of the pad is prone to shift. When this occurs, the adhesive force of the pad may fail to follow a load on it attributed to rotation of the edging tool, resulting in a phenomenon (axial deviation phenomenon) in which the attachment position of the pad shifts in the rotation direction.
To combat this situation, an adhesive pad which can stably attach onto even a water-repellent lens and withstand an edging load on it is under study.
Japanese Patent Laid-Open No. 2005-111612 (patent reference 2), for example, describes a technique for forming a grinding axial deviation preventive pad from a five-layered body including a first adhesive layer, cushion layer, bond layer, resin film, and second adhesive layer. The cushion layer has a thickness of 0.2 to 3 mm, an elongation of 150 to 500%, and a tensile strength of 5 to 200 kg/cm2. The bond layer has a bonding strength of 2,100 kg/25 mm. The resin film has an elongation of 50 to 700% and a tensile strength of 25 to 300 MPa. Such a technique described in patent reference 2 adjusts the thickness of the cushion layer to suppress damage inflicted on the lens when it is pressed by a lens fixing jig, and lowers the tensile strength of the cushion layer to suppress a phenomenon in which the adhesive surface floats (peels off) due to a load imposed on it by a rotary tool.
Japanese Patent Laid-Open No. 2004-330327 (patent reference 3) describes a technique for forming a lens fixing member from a composite adhesive sheet including a flexible double-sided adhesive cushion sheet and flexible single-sided adhesive sheet, brings the adhesion target surface of the single-sided adhesive sheet into press contact with one adhesive surface of the double-sided adhesive cushion sheet, and setting the bonding surface of the single-sided adhesive sheet to have a bonding area larger than that of the bonding surface of the double-sided adhesive cushion sheet. The technique described in patent reference 3 damps and absorbs, by the double-sided adhesive cushion sheet, impacts attributed to, e.g., pressing of the lens by the lens fixing jig and ensures a large attachment area of the flexible single-sided adhesive sheet, thereby attaching the cushion sheet onto a water-repellent lens surface. In other words, the technique described in patent reference 3 allows cutting of a water-repellent lens by stacking sheets of different roles on each other.
Japanese Patent Laid-Open No. 2004-249454 (patent reference 4) describes a technique associated with adhesive tape having an adhesive surface to come into contact with a lens. This technique adjusts the adhesive force of the adhesive surface of the tape such that its measurement value is 4 gf (0.0392 N) or more when an adhesion test according to the 180-degree peeling method stipulated in ISO29682 “Adhesive Tape/Adhesive Sheet Test Method” is conducted using a polyethylene terephthalate plate, with its surface treated by a fluorosilicone release agent, as a test plate. The technique described in patent reference 4 also specifies the adhesion strength of adhesive tape when it is peeled off at 180°. However, it is difficult to obtain an expected effect even by specifying the adhesive strength by its adhesive force acting upon its peel-off because the sheet itself is pressed by the lens fixing jig at the time of lens shaping.
Japanese Patent Laid-Open No. 2006-95657 (patent reference 5) is characterized by forming a minute opening in the adhesive surface of adhesive tape. Patent reference 5 also describes a mechanism in which the adhesive surface sticks onto the lens surface through the opening upon bonding them.
However, even the use of the tape described in patent reference 5 may result in an axial deviation when the adhesive surface floats due to entrance of water or air into the opening during edging.
Each of the lens pads described in patent references 2 to 4 described above is formed from a layered body including a soft adhesive layer and cushion layer. For this reason, a grinding load and a rotation moment remarkably concentrate on the adhesive surface. In this case, when a lens 3 fixed on a lens holder 1 through a pad 2 is attached onto a lens rotating shaft (not shown) and clamped by both the lens holder 1 and a lens retainer 4, as indicated by a solid line in FIG. 6, compressive deformation at the central portion of a cushion layer 5 of the pad 2 is large due to an edging load and a clamping pressure (chucking pressure) but that in the outer peripheral portion of the cushion layer 5 is small. Therefore, as the outer peripheral portion of a lens-side adhesive layer 6 separates and floats from a convex surface 3a of the lens 3, the adhesion area reduces and the original adhesion capacity of the adhesive surface degrades because the grinding fluid enters from the gap. This makes it difficult to perfectly prevent any axial deviation phenomenon of the lens 3. Note that an alternate long and two short dashed line 7 indicates the state of the pad 2 before its deformation.
The technique described in patent reference 5 leads to a reduction in area of the region where the adhesive layer sticks onto the lens surface through the minute opening. The peripheral portion of the opening serves as the boundary between the adhesive region and the non-adhesive region. The length of the boundary increases in proportion to the area of the adhesive region. The boundary between the adhesive region and the non-adhesive region becomes the point of origin where the tape floats from the lens surface. If the pad is attached onto a surface with a surface energy high enough to maintain a good adhesion state, the length of the boundary is less problematic. In contrast, if the pad is applied to a water-repellent lens surface with a low surface energy, the rate of occurrence of floating rises with increasing length of the boundary. This makes it impossible to maintain a good adhesion state in the adhesive region. When the pad is attached onto a water-repellent lens surface, the use of tape with a specification including a minute opening makes it impossible to maintain a tight contact state between the tape and the lens surface, resulting in an axial deviation phenomenon.